JPH07252597A - Continuous casting method of steel - Google Patents

Abstract

PURPOSE:To provide a method for securely producing a defectless slab at the time of subjecting a medium carbon steel to continuous casting. CONSTITUTION:This is a method for preventing depression and longitudinal cracks in a continuously cast slab in which components are regulated so as to satisfy the following conditions and subjected to casting at the time of subjecting a carbon steel and an alloy steel to melting and casting : A=-2.5[% C]-0.05-[%Mn]-0.1[%Ni]+-0.1[C]+0.25[%Si]+-[%Mo]+1.75[%S]+-1.25, and A <=0.95 or A >=1.05 is satisfied. Moreover, as for the basicity B of powder, in the case of A<0.90 or A>1.10, B is regulated to 0.8 to 1.4 and, in the case of 0.90<=A<=0.95 or 1.05 <=A<=1.10, B is regulated to 1.1 to 1.4. Thus, cracks and depression in a medium carbon steel can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing slab dents and vertical cracks generated in continuous casting of carbon steel, low alloy steel and the like.

[0002]

2. Description of the Related Art In continuous casting of steel, generally, molten steel is continuously poured into a water-cooled mold, and the molten steel injection amount is controlled to cast at a predetermined drawing speed. In continuous casting of steel, powder (CaO, SiO ₂ as a main component, Al ₂ O
₃ , which is composed of a component containing an oxide such as Na ₂ O) to form a molten state, and is allowed to flow between the mold and the slab for lubrication.

Since molten steel needs to be solidified in a mold, it is also necessary to properly maintain heat removal from the mold as a function of powder.

Therefore, in powder casting, it is general to perform forced vibration of the casting mold in the casting direction so that the lubricant can be uniformly introduced.

The uniform inflow of powder is necessary in order to uniformly grow the solidified shell.
Since 06-0.18 wt% C steel transforms from the δ phase to the γ phase during solidification and after solidification, the solidified shell is likely to be deformed due to the difference in the lattice structure. Vertical cracks may cause operational defects such as quality defects and breakouts.

Steel types having this carbon content are called medium carbon steel or hypoperitectic solidified steel. In addition, according to the experience of the present inventors, similar low-alloy steel having a relatively high carbon content of about 0.25 wt% C also experienced similar quality defects.

[0007] Conventionally, with respect to such problems peculiar to medium carbon steel, attempts have been made to improve the powder, and the countermeasures have been directed toward uniform inflow and slow cooling of heat removal from the mold.

However, improvement of the powder alone is not sufficient for quality assurance of cast slabs and elimination of operational troubles, and further stabilizing means have been demanded.

[0009] As a method for improving the surface defects of the slab of medium carbon steel, the Iron and Steel Institute of Japan "Materials and Processes" Vo
l. 4, No. 4 (1991) P1256-1257,
Similarly, P1284 can be exemplified.

The disclosure shows that mild cooling with powder is particularly effective in preventing vertical cracks and dent defects.

However, the disclosure merely shows the characteristics of the medium carbon steel and the effect of slowly cooling the powder, and does not suggest the importance of the combination of the casting components in terms of erasing the casting defects. , Only one aspect of the manufacturing technology for manufacturing on an industrial scale.

[0012]

DISCLOSURE OF THE INVENTION An object of the present invention is to disclose a concrete means capable of easily preventing defects such as medium carbon steel, which are likely to be accompanied by defects such as slab dents and vertical cracks. In view of the above, it is to discover that slab dents and vertical cracks are affected by the contents of molten steel components, especially carbon and alloying elements, and provide a concrete manufacturing method that can be realized on an industrial scale.

[0013]

Means for Solving the Problems The inventors of the present invention have noticed that the allowable range is set for the steel material components as is clear from the JIS standard, and the allowable range for the components of the medium carbon steel is within the allowable range. It was found that even fine adjustment had a great influence on the occurrence of defects, and the following conclusions were reached after repeated experimental studies on the solution of the problem of casting defects in medium carbon steel. That is, the gist of the present invention is

In carbon steel and alloy steel, C is 0.02 to
0.25% by weight, Si 0.01 to 1.8% by weight, Mn
Is 0.1 to 2.0% by weight, S is 0.001 to 0.08% by weight, Cr is 0.01 to 1.50% by weight, and Mo is 0.0.
1 to 0.50 wt%, Ni 0.01 to 1.00 wt%
And other trace elements and unavoidable impurities, the method for continuous casting of steel is characterized in that casting is performed after adjusting the components so as to satisfy the value A obtained by the following calculation formula. here,

[0015]

## EQU2 ## A = -2.5 [% C] -0.05 [% Mn]-
0.1 [% Ni] +0.1 [% Cr] +0.25 [% S
i] +0.25 [% Mo] +1.75 [% S] +1.2
5

Where A ≦ 0.95 or A ≧ 1.0
Satisfy 5.

When the above molten steel is continuously cast, 25 to 45% by weight of CaO and SiO ₂ are used as powder for continuous casting.
Is a powder whose main component is in the range of 25 to 40% by weight, and a basicity B (CaO / SiO ₂ ratio) is applied so as to satisfy the following conditions.

When A <0.90 or A> 1.10, B =
0.8-1.4, 0.90 ≦ A ≦ 0.95 or 1.05 ≦ A ≦ 1.10 and B = 1.1-1.4.

[0019]

The effects of the present invention will be specifically described.

First, the reason for limiting the component system will be described. As described above, it has been stated that slab dents and vertical cracks occur with specific components, but the specific component range is carbon steel and alloy steel, and C is 0.02 to 0.25% by weight. , Si is 0.01 to 1.8% by weight, and Mn is 0.1 to 0.1%.
2.0 wt%, S 0.001 to 0.08 wt%, Cr
Is 0.01 to 1.50% by weight, Mo is 0.01 to 0.5
0 wt%, Ni is 0.01 to 1.00 wt% and other trace elements and inevitable impurities.

The above-mentioned composition range is a composition range of carbon steel and alloy steel which cause the dent of a cast piece, and is also a composition range on which the present invention is premised, and the present inventors handle it through a casting test for an extremely long period of time. It is a steel type. Of course, it is expected that the above range will be established even if the above range is slightly exceeded.

Next, the value A calculated by the above components will be described. A is defined by the following formula.

[0023]

## EQU3 ## A = -2.5 [% C] -0.05 [% Mn]-
0.1 [% Ni] +0.1 [% Cr] +0.25 [% S
i] +0.25 [% Mo] +1.75 [% S] +1.2
5

From the experience of the present inventors, it was found that the surface quality of the slab is excellent in the range of A ≦ 0.95 or A ≧ 1.05, and no operational trouble such as breakout during casting occurs. There was found.

Although not particularly limited, it is desirable that A ≦ 0.90 or A ≧ 1.10 is effective in quality and trouble prevention.

However, in the range of 0.95 <A <1.05, slab dents, vertical cracks, and breakout occurred.

Therefore, it was found that a material of excellent quality can be supplied by adjusting the components so that the value of A falls within the above range, and the fine adjustment of the components can dramatically improve the surface quality of the cast slab. .

To explain the validity of the value A, it is exemplified how A changes. For example, C is 0.10 to 0.1
2% by weight, 0.25 to 0.30% by weight of Si, 1.0 to 1.2% by weight of Cr, and 0.015 to 0.030% by weight of S are acceptable component systems. Can be in the range of 1.14 to 1.25 if calculated using the above definition formula.

Therefore, it is clear that A can change sufficiently by about 0.1.

Next, a method for applying powder according to the value of A will be added to disclose a method for further improving the surface quality of the slab.

First, the components of the powder for continuous casting will be described.

The powder for continuous casting contains 25 to 45 CaO.
% By weight and SiO ₂ in the range of 25 to 40% by weight to form a powder which is the main component. This component range is not a special content for a continuous casting powder for steel, but is a component range investigated and confirmed by the present inventor.

Next, the powder basicity B (CaO
The reason for changing the ratio (/ SiO ₂ ratio) depending on the value of A will be described.

When the calculated value A is less than 0.90 or more than 1.10, the tendency of the slab to form dents becomes small, so that it is somewhat less affected by the powder, and the basicity B of the powder is investigated later. From the results, it is effective to set it to 0.8 to 1.4.

When the basicity is high, the solidification temperature becomes high and the lubricity is deteriorated, which may hinder high speed casting. Therefore, 0.8 to 1.1 is preferable, and when the amount of dents is severe, Is better to apply a higher value.

Therefore, by finely adjusting and changing A within the range of the specification that allows the molten steel component, high-speed casting is possible and a steel product of excellent quality can be manufactured.

On the other hand, 0.85 ≦ A ≦ 0.90 or 1.
In the case of 05 ≦ A ≦ 1.10, it approaches the component system in which dents are likely to occur. Therefore, it is effective to set the powder basicity to a slightly higher value and to set B = 1.1 to 1.4 according to the investigation result described later.

Of course, if A in this range, casting is possible even with low basicity, but the quality tends to deteriorate somewhat.

Specifically, in the range of A, B <1.1 powder sometimes causes cracks during cold forging, and the quality is not stable.

Therefore, if 0.85 ≦ A ≦ 0.95 or 1.05 ≦ A ≦ 1.2, it is desirable that B = 1.1 to 1.4, and a cold forging steel material can be manufactured without any problem. It was

As described above, the above contents generally hold and need not be limited, but as shown in the examples described later, a slab size of about 162 × 162 mm and a minimum cross section of about 200 × 200 mm. The combination of the component adjustment index A and the powder basicity B is effective when performing continuous casting at a high speed of about 1.5 to 3.5 m / min. The present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing a combination of the occurrence ratio of slab dents and A calculated from molten steel components and powder basicity B. The plots in the figure show the conditions stratified by powder basicity described below.

FIG. 2 is an explanatory view showing the relationship between the rate of occurrence of vertical slab cracking and A and the influence of powder basicity B.

It can be seen from FIG. 1 that the cast dent has a close relationship with the calculated value A, and there is a region for preventing the dent due to A. Further, it can be seen that the range in which the depression can be prevented differs depending on the powder basicity B.

Therefore, it can be seen that if A is changed according to the component amount of carbon steel or alloy steel and combined with an appropriate basicity B, cast products and products without defects can be manufactured.

From FIG. 2, the slab vertical cracking occurrence rate can be arranged by the value A in consideration of the influence of the components similarly to the slab dent, and it is possible to find a component condition for preventing the vertical cracking occurrence rate. .

[0047]

EXAMPLES The present invention will be described below with reference to specific examples.

Main components and powder components of carbon steel and alloy steel used for casting are as shown in Tables 1 and 2.

The casting conditions are shown below.

Examples are carbon steels having the above molten steel composition ranges,
Using low alloy steel, all slab size 162mm × 162
mm continuous casting machine was used.

The casting speed is 1.6 m / min to 3.2 m
The range is / min.

The degree of superheat of molten steel is 25 to 25 in the tundish.
It was carried out in the range of 40 ° C.

FIG. 1 is an explanatory view in which a combination of a cast dent occurrence rate index and a value A calculated by the molten steel component and a combination of powder basicity B are plotted. In addition, the plot shows the effect of the powder basicity B by stratification.

The horizontal axis represents the value of A, and the vertical axis represents the cast dent occurrence rate index. When the index value is 0, no slab dent is generated, and when the number is less than 100, there is no slab crack described later, and no defects will occur in the subsequent hot rolling or product processing such as cold forging by the user. I know.

From FIG. 1, the slab dent has a close relationship with the value A, and the value of A can represent the condition for preventing the slab dent.

Therefore, by changing A by finely adjusting the composition of the steel type, it is possible to manufacture a cast slab without depressions. Also,
Proper combination of powder basicity B is effective.

FIG. 2 shows the relationship between the incidence rate of vertical slab cracking and A and the powder basicity. The effect of powder basicity is shown in the same plot as in FIG.

From FIG. 2, it can be seen that the rate of occurrence of vertical cracks in the slab changes depending on the value of A, and vertical cracks can be prevented by defining A, that is, adjusting the casting composition.

Next, the relationship between the calculated value A obtained from the components and the powder basicity B (CaO / SiO ₂ ratio) will be explained. Increasing the degree B was effective.

As described above, the tendency of pitting is predicted by the value of A, and the pitting tendency is large, that is, the basicity is increased as A approaches 1.0, the solidification temperature is raised and the heat removal from the mold is slowly cooled. It is thought to mean that it is necessary to

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

As described above, by adjusting the molten steel composition according to A of the present invention, it is possible to reduce slab dents and vertical cracks, and by optimizing the powder application conditions, it is possible to reduce dents and vertical cracks. It was shown concretely that it is possible to produce a slab with excellent surface quality and no slab.

Therefore, the method of the present invention enables stable casting of steel materials, has a high product yield, and enables the supply of cheaper products, which can be said to be an extremely useful invention in industry.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a cast dent dent occurrence rate index and A obtained from a molten steel component.

FIG. 2 is an explanatory diagram showing a relationship between a vertical slab occurrence rate and A.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masashi Yoshida 12 Nakamachi, Muroran City Muroran Works, Muroran Works (72) Inventor Takeyuki Sekiya 12 Nakamachi, Muroran-shi Muroran Shin Nippon Steel Co., Ltd. Inside the steelworks

Claims (2)

[Claims] 1. A continuous casting method for steel, wherein when the components of carbon steel and alloy steel are within the following ranges, the components are adjusted so that the value A determined by the following calculation formula is satisfied, and then the casting is performed.
C is 0.02 to 0.25% by weight, and Si is 0.01 to 1.
8 wt%, Mn 0.1-2.0 wt%, S 0.00
1 to 0.08 wt%, Cr 0.01 to 1.50 wt%, Mo 0.01 to 0.50 wt%, Ni 0.01
.About.1.00% by weight and other trace elements and unavoidable impurities, the following expression is obtained: A = -2.5 [% C] -0.05 [% Mn]-
0.1 [% Ni] +0.1 [% Cr] +0.25 [% S
i] +0.25 [% Mo] +1.75 [% S] +1.2
5 and satisfies A ≦ 0.95 or A ≧ 1.05. Here, each symbol is an alloy element name and weight concentration of carbon steel or alloy steel. 2. When continuously casting the molten steel according to claim 1, 25 to 45% by weight of CaO and SiO are used as powder for continuous casting.
_2. A continuous casting method for steel, characterized in that powder ₂ is a main component in the range of 25 to 40% by weight, and basicity B (CaO / SiO ₂ ratio) is applied so as to satisfy the following conditions. . If A <0.90 or A> 1.10, B =
0.8 to 1.4, and if 0.90 ≤ A ≤ 0.95 or 1.05 ≤ A ≤ 1.10, B = 1.1 to 1.4.